The biocompatibility requirements for implantable medical devices are quite high. The materials of which they are made or impurities in those materials should not cause or contribute to inflammatory responses, immunological responses or any other undesirable side effects. Regulatory requirements further stipulate that permanently implanted materials be of high purity.
Implantable medical devices, particularly stents, have been developed for use in the local administration of therapeutic substances to a diseased site. These devices may be fabricated from a biocompatible polymer and a therapeutic substance can be incorporated in the body of the device or they may be coated with a biocompatible polymer containing the therapeutic substance. If a coating is used, it too, must have the biocompatibility characteristics mentioned above.
Commercially available polymers that might be useful in the production of implantable medical devices or for coatings on such devices can contain impurities that can trigger adverse biological responses in a patient. For example, the polymers may contain impurities such as catalysts, initiators, processing aids, suspension aids, unreacted monomers, metal salts, low molecular weight oligomers and the like. To ameliorate this situation, commercial polymers are often purified by the implantable medical device manufacturer prior to use. Many of the processes employed to purify polymers, however, are time consuming, costly and inefficient. The present invention provides a cost effective, efficient method for the purification of one such family of polymers, poly(ethylene-co-vinyl alcohol) copolymers.